Important Questions of Ray Optics and Optical Instruments Physics | Zigya

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61.

A red coloured object illuminated by mercury vapour lamp, when seen through a green filter, will appear

  • red

  • blue

  • black

  • white


62.

Time taken by sunlight to pass through a window of thickness 4 mm whose refractive index is 32 is

  • 2 × 10-4 s

  • 2 × 104 s

  • 2 × 10-11 s

  • 2 × 1011 s


63.

Two thin lenses of focal length 20 cm and 25 cm are in contact. The effective power of the combination is

  • 4.5 D

  • 18 D

  • 9 D

  • 2.5 D


64.

The magnification of the image when an object is placed at a distance x from the principal focus of a mirror of focal length f

  • xf

  • 1 + fx

  • fx

  • 1 - fx


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65.

If n1 and n2 are the refractive indices of the core and the cladding respectively of an optic fibre, then

  • n1 = n2

  • n1 < n2

  • n <  n1

  • n2 = 2n1


66.

A fish at a depth of 12 cm in water is viewed by an observer on the bank of a lake. To what height the image of the fish is raised ? (Refractive index of lake water = 4/3). 

  • 9 cm

  • 12 cm

  • 3.8 cm

  • 3 cm


67.

A ray of light is incident at 50° on the middle of one of the two mirrors arranged at an angle of 60° between them. The ray then touches the second mirror, gets reflected back to the first mirror, making an angle of incidence

  • 50°

  • 60°

  • 70°

  • 80°


68.

A lamp (point source) is hanging along the axis of a circular table of radius r. At what height should the lamp be placed above the table so that the illuminance at the edge of the able is 18 of that at its centre ?

  • r2

  • r2

  • r3

  • r7


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69.

The focal length (f) of a spherical (concave or convex) mirror of radius of curvature R is

  • R2

  • R

  • 32R

  • 2R


70.

In a compound microscope, the intermediate image is

  • virtual, erect and magnified

  • real, erect and magnified

  • real, inverted and magnified

  • virtual, erect and reduced


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